The present invention relates to a reflective-type liquid crystal display device and a reflecting substrate thereof, and more particularly to the reflective-type liquid crystal display and the reflecting substrate having an improved reflective luminance in the main viewing angle directions of the user.
A liquid crystal display device (LCD) has been widely used for a display device of a portable television and a notebook computer. The liquid crystal display device is classified into two types: a transmitting-type liquid crystal display device using a backlight as a light source; and a reflective-type liquid crystal display device using an external light source such as sunlight and an indoor lamp. It is hard to decrease the weight, volume, and the power consumption of the transmitting-type LCD because of the backlight. Accordingly, a great deal of research has been done regarding the reflective-type LCD.
Conventionally, the reflective-type LCD uses a reflecting substrate having an uneven reflecting surface to enlarge the viewing angle of the user. FIG. 1a is a plane view showing the conventional reflective-type LCD, and FIG. 1bis a sectional view taken along line I-Ixe2x80x2. As shown in the figures, the reflective-type LCD comprises a substrate 1, round bumbs 2 on the substrate 1, and an overcoat layer 3 over the round bumps 2, and a metal layer on the overcoat layer 4.
The reflective-type LCD is manufactured by the following processes. First, a photoresist layer is formed on the substrate 1, and UV light is irradiated into the photoresist layer with a mask blocking the photoresist and having holes in the same plane form as the round bumps 2 as shown in FIGS. 1a and 1b. Thereafter, the photoresist layer is developed and heat-treated to form the round bumps 2 on the substrate 1. Continually, the overcoat layer 3 is coated on the round bumps 2 to obtain a continuous convex-concave surface. Finally, the metal layer 4 is formed thereon by sputtering metal such as Al, Mo, and Al alloys. The metal layer 4 has a continuous convex-concave surface as the overcoat layer 3, and functions as reflecting and scattering the incident light into various directions. Accordingly, an LCD using the conventional reflecting substrate has a wide viewing angle of the user.
However, a large amount of light reflects except in the main viewing angle direction of the user, so that the reflectivity is very low in the main viewing angle direction. Further. as shown in FIG. 6a, the plane of incidence does not match with the plane of reflection at the side of the convex surface, and thereby the polarization direction is changed to cause the wrong operation of the device. Dotted lines in this figure represent the polarization directions. Furthermore, two forming steps of the round bumps and the overcoat are required to obtain the continuous convex-concave surface, thereby complicating the manufacturing process.
An object of the present invention is to provide a reflective-type liquid crystal display device and a reflecting substrate thereof having an improved reflective luminance in the main viewing angle direction.
In order to achieve the object, the reflecting substrate according to the present invention comprises: a substrate parallel to first and second directions perpendicular to each other; an insulating layer having a convex-concave surface over the substrate, a convex portion thereof having a first width in the first direction and a second width in the second direction, the first outline having first and second width perpendicular to each other, the first width being larger than the second width, the convex portion having a straight outline in a plane perpendicular to the substrate and parallel to the first direction, and the convex portion having a round outline in a plane perpendicular to the substrate and parallel to the second direction; and a metal layer on the convex-concave surface of the convex-concave insulating layer.
In order to achieve the object, a reflective-type liquid crystal display device according to the present invention comprises: first and second substrates parallel to first and second directions perpendicular to each other; an insulating layer having a convex-concave surface over the first substrate, a convex portion thereof having a first width in the first direction and a second width in the second directions, the first outline having a first and second width perpendicular to each other, the first width being larger than the second width, and the convex portion having a round outline in a plane perpendicular to the first substrate and parallel to the second direction; a metal layer on the convex-concave surface of the insulating layer; a first alignment layer over the metal layer and having a first alignment direction; a polarizer over the second substrate and having a polarization direction parallel to the second direction; an optical film for phase retardation of light over the second substrate, the optical film being at a position between the polarizer and the first substrate; a second alignment layer over the second substrate and having a second alignment direction; and a liquid crystal layer between the first and second alignment layers.
When light is incident to the metal layer, a large amount of light reflects into the main viewing angle direction by the inventive shape of the convex-concave surface which the metal layer has.
It is preferable that the polarization direction is at 90xc2x0 with respect to the first direction, and slow axis of the optical film is at 45xc2x0 with respect to the polarization direction. In this case, TE(transverse electric) mode light is incident on the metal layer, so that the reflectance is much more improved. Further, because the incidence plane is match with the reflectance plane on the metal layer, the polarization of the light is not changed after it is reflected on the metal layer.